Summary of Work: This project includes those endeavors in which the mass spectrometry workgroup collaborates with other groups, both inside and outside the Institute to solve problems of mutual interest. The major focuses of these projects are: 1) structure determination of unknown compounds; 2) identification and/or confirmation of biological pathways; 3) quantitation; and 4) development of strategies for the structure determination of biologically important compounds. Current major collaborative projects under way include: 1)quantitation of hydroxyoctadecadienoic acid and hydroxyeicosanoic acids in cells; 2) quantitation of arachidonic acid metabolites (D. Zeldin, LPP). Quantitation of Arachidonic Acid Metabolites - The most sensitive and accurate method for quantitation of eicosanoids in physiological samples is by selected ion monitoring (SIM) under negative ion chemical ionization (NICI) mass spectrometry. We are currently quantifying eicosanoid metabolites as part of several studies. These include: Characterization of the arachidonic acid metabolites of a new cytochrome P450, CYP2J5, isolated from a mouse liver cDNA library and abudantly expressed within tubules of the renal cortex. CYP2J5 arachidonic acid oxidation products are postulated to play important functional roles in the kidney. Determination of the variations in arachidonic acid metabollism as a function of changes in P450 function occurring during fasting and refeeding in rats. Characterization of arachidonic acid metabolites in fish as characterization of the alteration of endogenous arachidonic acid metabolism as a function of being challenged with TCDD and BP. Characterization of the CYP2J subfamily cytochrome P450s in the human jejunum. 15-lo is highly expressed in human colorectal tumors. The function of 15-lo expression is being investigated in caco-2 cells. The 15-lo is expressed during Na butyrate induced apoptosis and cell differentiation. Inhibition of 15-lo enhances the NaBT induced apoptosis. Metabolism studies using cell lysates indicate a shift in exogenous metabolism of AA and LA to 15-HETE and 13-HODE. The time course for the formation of 15-HETE and 13-HODE during the induction of cell differentiation and apoptosis is being determined as a means of determining the function of 15-lo expression in these cells.